1. Field of Invention
The present invention relates, in general, to an automatic transmission, and more particularly, to the structure of a multi-stage automatic transmission which is disposed in a vehicle and can provide a plurality of transmission gear ratios.
2. Description of Related Art
In general, the multi-stage transmission mechanism of an automatic transmission is realized by combining a plurality of planet gears and friction elements. Because a vehicle having more excellent power performance and fuel efficiency can be realized when more shift ranges can be realized, studies on automatic transmissions which can realize more shift ranges are constantly underway.
In addition, even at the same shift range, the endurance, power transfer efficiency, size and the like of a gear train vary depending on the way that the plurality of planet gears and the friction numbers are combined. Therefore, attempts to invent a gear train structure which is stronger, consumes less power and is more compact have been made and are currently underway.
In addition, when a plurality of shift ranges are provided, at a viewpoint of shift control, whether or not a shift gear operation condition for disabling one friction element and enabling the other friction element during sequential shifting to the adjacent shift range is satisfied, and whether or not the shift ratio and range ratio between adjacent shift gears are of suitable levels, are two conditions gaining interest as distinctive functions in the field of gear trains. In addition, attempts to invent a gear train structure which satisfies such functions are underway.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.